1. Field of the Invention
The present invention relates to a successively-deciding production planning system for efficiently planning the production of products, the required number of parts, and the material arrangement according to the required number of parts and required period.
2. Description of the Related Art
It is the function of a production plan to determine three factors of the type of product to be produced, the quantity, and the period by reflecting product orders and demand forecast. However, the production plan is frequently modified due to the fluctuation of product orders and demand forecast values. Because production preparation including parts arrangement requires some preceding lead time for the point of time for actual production, it is necessary to make a plan in view of a relatively long time from the present to the future by considering the preceding lead time. For sales forecast data such as product orders and demand forecast, however, further information has more indeterminate factors. Therefore, the production plan should be reviewed according to the elapse of time.
The existing production planning system generally uses a method for allocating a production quantity to a time schedule representing a production period equally divided at a certain interval. For this method, however, the production quantity per day for the near future (e.g. 2 days ahead) is greatly different from that for the far future (e.g. one month ahead) in the actual certainty. A product generally belongs to a family formed by collecting similar products in view of the structure and several families are further collected for assortment of products as the entire product group including many ranks of products from lower to higher ranks. For example, higher-rank type of product is a group of plurality of lower-rank types of product. And, in the other example, a higher-rank type of product is a standard type of product and a lower-rank type of product is a variation of the higher-rank type of product. For sales forecast data, further information has higher accuracy for the level of higher-rank type of product but lower accuracy for the level of lower-rank type of product. However, a production plan is frequently made for the level of the lowest-rank type of product. Moreover, a type of product for the near future is greatly different from that for the far future in the certainty. Therefore, for the existing production planning system, production quantity and type of product are equally handled as pieces of designation information having no difference in the accuracy in a time schedule representing the production period.
For the existing production planning system, as described above, planned production values (e.g. type of product to be produced and quantity) with lower certainty further allocated are frequently modified. In this case, it is difficult to keep the overall consistency by correcting only the value to be modified. Therefore, a production plan may be modified to an inexecutable plan in view of the lead time for part arrangement or to a plan having large loss as a whole. To avoid this error, a method is used to make an executable and optimum production-plan modification plan by repeatedly performing the calculation for the required material quantity plan based on a production-plan modification plan and previous evaluation of the plan. However, the calculation for the required material quantity plan becomes a bottle neck because it requires a very long time. Therefore, the production plan is frequently modified before it is adequately evaluated. According to the above plan modification, required number of parts and materials are planned and these planned values are sent to the production lines, users, and suppliers of the company concerned as modification designation information. Oversupply of the modification information including the above problems causes disorder of production lines, delay of delivery deadline, and decrease of productivity.
The problems of the existing production planning system are described below in detail by referring to FIGS. 14 and 15. FIG. 14 shows an existing production plan. This plan is made in the last ten days of March, in which the production quantity for three months from April to June is planned for each ten days of a month and each type of product. The plan for April close to the point of time the plan is made and the plan for June which is the near future are expressed as data of the same format with no difference in accuracy. When a production plan is made, production preparation securing a proper lead time must be performed (e.g. arrangement of parts, securing of production capacity, and subcontract). For the plan for June in FIG. 14, it is necessary to execute the production preparation duties including a two-month lead time. Preparation duties for June production to be executed according to this production plan are described at the right of FIG. 14. For example, when a part requiring the delivery period of two months is arranged by using the planned values for June (production preparation &lt;1&gt;). Moreover, if a two-month lead time is also necessary to secure the production capacity, a line working plan for June is made and actions for securing a necessary production capacity must be taken (production preparation &lt;2&gt;). Further more, it is necessary to order products from an external affiliated factory (production preparation &lt;3&gt;).
FIG. 15 shows the details of production planning a ten-day period after the period in FIG. 14. In this case, a plan for three months from the middle ten days of April to the first ten days of July is made. First, a rough production plan is made according to demand forecast and received order information (Processing 1). Then, this plan is compared with the plan made last time to check if a large modification is made (Processing 2). Especially, the contents of the production preparation in the latest plan or the processing in the last ten days of March cannot be greatly modified. Therefore, it is necessary to check the modification degree. For example, checking with the production capacity of the working plan made last time and checking of the delivery period of the subcontracted type of product are necessary. The above mentioned is the checking of product quantity. However, it is necessary to check the quantity level of parts necessary for products. Summing the number of parts necessary for each type of product is called the required material quantity calculation which is normally performed by a computer because the operation requires a large calculation load.
After the required quantity of each type of part is calculated, the modification degree is checked at the part quantity level with the latest production plan (Processing 4). For example, it is necessary to check if the number of parts already ordered is exceeded. If a trouble occurs in the product quantity level checking (Processing 2) or part quantity level checking (Processing 4), the production plan is corrected and the same processing is repeated once again. For example, because the delivery deadline of 100 parts of the type of product D in FIG. 15 is 2 ten-day periods earlier than that in FIG. 14, it becomes NG in the subcontracted type-of-product delivery deadline checking of Processing 2. Though this example is described by using simple values, actually necessary checking is complex. In the number-of-part checking, for example, it is necessary to check not only the period quantity (quantity for June) but the cumulative quantity (cumulative quantity from April to June). The existing production planning system described above has the following problems.
Problem 1: Further production plan is extremely minute and the number of data values is too many. That is, as shown in FIG. 14, the production preparation using the further production plan includes a line working plan (capacity plan) and part ordering, which frequently uses macro information such as monthly total and total of type-of-product groups compared with the very near plan. For example, the production preparations &lt;1&gt; and &lt;2&gt; in FIG. 14 are performed by using the total value in June. This is because the accuracy of macro information is higher than that of detailed information though detailed production plan information is frequently modified later even if it is used. However, all existing production plans require a large amount of data because they are expressed with micro information.
Problem 2: It takes a lot of time to check the possibility for modification of a production plan. That is, because calculations except the development of the required number of parts (Processing 3) in FIG. 15 are performed by hand, it takes a lot of time. Even the calculation of the required number of parts requires a lot of time because the actual number of types of products amounts to hundreds to thousands and the actual number of types of parts amounts to thousands to hundreds of thousands.
Problem 3: A production plan is modified before it is adequately checked. That is, the time for production planning is greatly shortened because the request for short delivery period has been increased in recent years. For example, when collection of received order information necessary for production planning and arrangement and calculation of materials based on production plan information are performed according to a predetermined time schedule, a production plan must be made during the period. Moreover, it takes a lot of time to develop the required number of parts as previously mentioned. For example, if three days are allowed for production planning and parts development can be performed by a computer only once in the nighttime, checking up to the part level can be performed only two to three times. Therefore, the production plan is forwarded before it is adequately checked. According to the plan modification, the required number of parts and material arrangement are planned and transferred to the production lines, suppliers, and subcontractors of the company concerned as modification designation information. Oversupply of the modification information including the above problems causes disorder of production lines, delay of delivery deadline, and decrease of productivity.
Problem 4: A production plan cannot be made which adequately reflects demand forecast and received order information. That is, as described in Problem 3, a production plan not adequately reviewed is made, causing troubles such as delay of delivery to users.
Problem 5: The criteria for modification checking is not clear. That is, because the modification checking criteria shown in FIG. 15 lies in the brain of the person in charge of production planning, it is impossible to quantitatively obtain the modification possibility from a shown production plan. In general, the modification degree is experientially estimated in an affiliated factory or parts machining line. Though the modification degree can be previously determined as an operation rule, it is difficult to completely observe the rule unless there is sufficient time for production plan modification checking. The present invention is made to solve the above problems and an object is to provide a successively-deciding production planning system capable of preventing disorder of production lines due to oversupply of improper modification designation information caused by production plan modification, realizing efficient calculations (required material quantity plan, material arrangement plan, and arrangement information designation) with a computer, and solving the above five problems.